AWWA WQTC62375

Metropolitan Water District of Southern California (Metropolitan) is a water wholesaler supplying more than 50-percent of drinking water to over 17-million people in southern California. Metropolitan operates five regional water treatment plants (WTPs) that use conventional coagulation, sedimentation, and multi-media (e.g., anthracite, sand) filtration with a combined design flow capacity of more than 2.5 billion-gallons-per-day. To comply with disinfectants and disinfection byproducts (D/DBP) regulations set by the U.S. Environmental Protection Agency, Metropolitan is retrofitting its WTPs with pre-ozone (upstream of conventional treatment) disinfection. Following ozone retrofit, subsequent chlorination is postponed until after filtration, allowing filters to operate in a biologically-active manner (biofiltration). This allows for biodegradable organic matter (BOM), produced by ozonation, to be significantly reduced prior to distribution. Metropolitan's H.J. Mills WTP began biofiltration in August 2004 and currently operates biofilters with a 70-percent BOM reduction goal. This manuscript summarizes results from the first year of biofilter operations, including: BOM removal, bacterial sloughing, effects on filter run length, and effect on the level of WTP-effluent, halogenated DBPs. Includes 14 references, tables, figures.